Technical Field of the Invention
The present invention relates to a universal gearbox mechanism featuring cam-actuated gear block assemblies that periodically engage the output gear causing power transfer. It has particular, but not exclusive, application for use in servomotor assemblies.
Description of the Related Art
Conventional machines typically consist of a power source and a power transmission system, which provides controlled application of the power. A variety of proposals have previously been made in the art of power transmission systems. The simplest transmissions, often called gearboxes to reflect their simplicity (although complex systems are also called gearboxes in the vernacular), provide gear reduction (or, more rarely, an increase in speed), sometimes in conjunction with a change in direction of the powered shaft. A transmission system may be defined as an assembly of parts including a speed-changing gear mechanism and an output shaft by which power is transmitted from the power source (e.g., electric motor) to an output shaft. Often transmission refers simply to the gearbox that uses gears and gear trains to provide speed and torque conversions from a power source to another device.
Gearboxes have been used for many years and they have many different applications. In general, conventional gearboxes comprise four main elements: power source; drive train; housing and output means. The power source places force and motion into the drive train. The power source may be a motor connected to the drive train through suitable gearing, such as a spur, bevel, helical or worm gear.
The drive train enables the manipulation of output motion and force with respect to the input motion and force provided by the power source. The drive train typically comprises a plurality of gears of varying parameters such as different sizes, number of teeth, tooth type and usage, for example spur gears, helical gears, worm gears and/or internal or externally toothed gears.
The gearbox housing is the means which retains the internal workings of the gearbox in the correct manner. For example it allows the power source, drive train and output means to be held in the correct relationship for the desired operation of the gearbox. The output means is associated with the drive train and allows the force and motion from the drive train to be applied for an application. Usually, the output means exits the gearbox housing.
The output means typically can be connected to a body whereby the resultant output motion and force from the drive train is transmitted via the output means (e.g., an output shaft) to the body to impart the output mean's motion and force upon the body. Alternatively, the output means can impart the motion and force output from the drive train to the gearbox housing whereby the output means is held sufficiently as to allow the gearbox housing to rotate.
Rotating power sources typically operate at higher rotational speeds than the devices that will use that power. Consequently, gearboxes not only transmit power but also convert speed into torque. The torque ratio of a gear train, also known as its mechanical advantage, is determined by the gear ratio. The energy generated from any power source has to go through the internal components of the gearbox in the form of stresses or mechanical pressure on the gear elements. Therefore, a critical aspect in any gearbox design comprises engineering the proper contact between the intermeshing gear elements. These contacts are typically points or lines on the gear teeth where the force concentrates. Because the area of contact points or lines in conventional gear trains is typically very low and the amount of power transmitted is considerable, the resultant stress along the points or lines of contact is in all cases very high. For this reason, designers of gearbox devices typically concentrate a substantial portion of their engineering efforts in creating as large a line of contact as possible or create as many simultaneous points of contacts between the two intermeshed gears in order to reduce the resultant stress experienced by the respective teeth of each gear.
Another important consideration in gearbox design is minimizing the amount of backlash between intermeshing gears. Backlash is the striking back of connected wheels in a piece of mechanism when pressure is applied. In the context of gears, backlash (sometimes called lash or play) is clearance between mating components, or the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established. For example, in a pair of gears backlash is the amount of clearance between mated gear teeth.
Theoretically, backlash should be zero, but in actual practice some backlash is typically allowed to prevent jamming. It is unavoidable for nearly all reversing mechanical couplings, although its effects can be negated. Depending on the application it may or may not be desirable. Typical reasons for requiring backlash include allowing for lubrication, manufacturing errors, deflection under load and thermal expansion. Nonetheless, low backlash or even zero backlash is required in many applications to increase precision and to avoid shocks or vibrations. Consequently, zero backlash gear train devices are in many cases expensive, short lived and relatively heavy.
Weight and size are yet another consideration in the design of gearboxes. The concentration of the aforementioned stresses on points or lines of contact in the intermeshed gear trains necessitates the selection of materials that are able to resist those forces and stresses. However, those materials are oftentimes relatively heavy, hard and difficult to manufacture.
Thus, a need exists for an improved and more lightweight gearbox mechanism, which is capable of handling high stress loads in points or lines of contact between its intermeshed gears. Further, a need exists for an improved and more lightweight gearbox mechanism having low or zero backlash that is less expensive to manufacture and more reliable and durable.